JP2012510440A - Method for removing by-products from N-vinylamide - Google Patents

Abstract

  In the method for separating a by-product from a product mixture rich in N-vinylamide (crude N-vinylamide), the extraction of the crude N-vinylamide is carried out using an organic solvent as an extractant. how to.

Description

  The present invention relates to a method for separating by-products from a product mixture rich in N-vinylamide (Roh-N-Vinylamid), the method extracting the extraction of the crude N-vinylamide. It implements using the organic solvent as an agent.

  Processes for the production of N-vinylamides such as N-vinylpyrrolidone are described, for example, in DE-A 10255437, DE-A 19509362 and DE-A 19395565. Due to the production process, the resulting product mixture is a series of various by-products such as starting materials, already formed oligomers or polymers of vinyl compounds and, in particular, chemical transformations in the reactor. Contains other by-products that may be generated in practice. The latter also includes fluoreszierende Nebenprodukte, which is not removed or only incompletely removed by conventional distillation purification of the product mixture.

  These fluorescent by-products degrade product quality. Therefore, what is desired is a simple method that removes these fluorescent byproducts as completely as possible from the product mixture.

  Accordingly, the method defined at the beginning has been found.

  In the process according to the invention, by-products are separated by extraction from a product mixture rich in N-vinylamide (crude N-vinylamide).

のビニルアミドであってよい。 About Crude N-vinylamides N-vinylamides are cyclic N-vinylamides (vinyl lactams) or acyclic N-vinylamides such as the formula

Of vinylamide.

  In formula I, R1 and R2 are independently of each other an H atom or a C1-C10 alkyl group, preferably C1-C4 alkyl.

  Acyclic N-vinylamides of the formula I include in particular N-vinylformamide (R1 and R2 = H) and N-vinyl-N-methylacetamide (VIMA, R1 and R2 = methyl).

  Examples of vinyl lactams include N-vinyl piperidone, N-vinyl caprolactam, N-vinyl pyrrolidone or derivatives thereof. The derivatives are in particular vinyl lactams, in which one or more, preferably one or two, carbon atoms of the ring structure are replaced by C1-C10 alkyl groups, in particular N-vinylmethyl. Examples include pyrrolidone, N-vinyldimethylpyrrolidone, and N-vinylethylpyrrolidone.

  Particularly preferred N-vinyl amides are vinyl lactams, in particular N-vinyl caprolactam or N-vinyl pyrrolidone.

  A very advantageous N-vinyl amide is N-vinyl pyrrolidone.

  According to the invention, crude N-vinylamide is extracted. Crude N-vinylamide is understood as a product mixture rich in N-vinylamide. This may be a product mixture that occurs as a product of chemical transformation in the reactor, is subsequently removed as reactor output and fed directly to the extraction. In the case of N-vinylpyrrolidone, this is preferably a product mixture obtained by reaction of 2-pyrrolidone (γ-butyrolactam) with acetylene.

  However, it may also be a crude N-vinylamide from other production methods, for example as described on page 5 in WO 2006/109869. Crude N-vinylamide can be obtained, for example, by reaction of butyrolactone with ethanolamine, replacement of hydroxy group with chloride using thionyl chloride and subsequent dehydration or reaction of N- (2-hydroxyethyl) -2-pyrrolidone with acetic anhydride. And removal of acetic acid or vapor phase dehydration of N-hydroxyethyl-2-pyrrolidone.

  The crude N-vinylamide used for the extraction may be a product mixture that has already been further worked up after conversion in the reactor in order to remove starting materials or by-products.

  In particular, crude N-vinylamides, such as crude N-vinylpyrrolidone, are mixtures obtained by reaction of starting materials such as 2-pyrrolidone with acetylene and, optionally, subsequent workup of the resulting product mixture. .

  In general, the mixture used for extraction as crude N-vinylamide comprises at least 50% by weight, particularly preferably at least 70% by weight and in particular at least 80% by weight, of N-vinylamide.

  In the case of N-vinylpyrrolidone, it is particularly advantageous to obtain first by reaction of acetylene with 2-pyrrolidone, from which subsequently high boilers (for example oligomers of N-vinylpyrrolidone) are first distilled ( Crude N-vinyl pyrrolidone separated by (Rohdestillation) is used. The distilled-off mixture contains N-vinylpyrrolidone, generally in an amount of more than 70% by weight, particularly preferably in an amount of more than 80% by weight, and the remaining 2-pyrrolidone (generally 0 to 30% by weight, particularly preferably 1 to 25% by weight) and by-products having a boiling point higher than the 2-pyrrolidone are generally in an amount of 0.5 to 20% by weight, particularly preferably 0. It is contained in an amount of 5-10% by weight, in which case all the mass data given above are for the mixture. This mixture is used in a particularly advantageous embodiment as crude N-vinylpyrrolidone for subsequent extraction.

  The crude N-vinylamide used for extraction, for example crude N-vinylpyrrolidone, contains in particular fluorescent by-products. These by-products are considered to be aromatic compounds having a boiling point (at standard pressure) of 150-320 ° C, in particular 200-260 ° C.

About extractant In the extraction, an organic solvent is used as an extractant.

  The by-product to be separated should be as well soluble as possible in the solvent. At the same time, the solvent must not be miscible with the mixture to be extracted under extraction conditions, or may be only slightly miscible, so that two phases are formed. The binary phase diagram from the mixture to be extracted and the extractant must have a solubility gap under the extraction conditions.

  If the crude N-vinylamide does not have a solubility gap with the extractant, a mixture with a corresponding solubility gap can be used instead of the crude N-vinylamide. The mixture components should be as miscible as possible with the crude N-vinylamide, as miscible as possible with the extractant, and easily separable from the crude N-vinylamide after extraction. is there. A preferred mixture component is water. This may be water containing dissolved inorganic or organic salts.

  In an advantageous embodiment of the invention, the extraction is carried out with the addition of water. The extractant then consists of water and one or more organic solvents. The extractant consists, for example, of 1-70% by weight of water, in particular 2-50% by weight.

  Suitable as extractants are, for example, aromatic solvents such as benzene, toluene or xylene (isomer mixtures). However, aromatic solvents are often not desired. Furthermore, in this case, N-vinyl pyrrolidone is partially transferred to the organic phase, so that complete separation of N-vinyl pyrrolidone is not performed.

  As organic solvents for the extractant, in particular aliphatic or cycloaliphatic solvents are suitable. Particular preference is given to aliphatic or cycloaliphatic solvents which have a boiling point higher than 80 ° C. (at 1 bar), which is liquid at 21 ° C. (1 bar). In particular, they are completely nonpolar solvents, ie (hydrocarbon) compounds consisting only of carbon and hydrogen.

  The above-mentioned aliphatic or cycloaliphatic solvents can of course also be used in the form of mixtures with aromatic solvents. The content of aromatic solvents in the total amount of all organic solvents used in the extractant is particularly preferably less than 50% by weight, in particular less than 30% by weight, particularly preferably from 10% by weight. Small or less than 5% by mass. In one particularly advantageous embodiment, the organic solvent used as the extractant does not contain an aromatic solvent.

  Examples of suitable aliphatic or alicyclic solvents are, for example, methylcyclopentane, cyclopentane, hexane, methylcyclohexane, cyclohexane, heptane or octane. Suitable solvents are in particular compounds having a solubility gap with the N-vinylamide to be extracted. Mixtures of various solvents can also be used as the extractant; for example, a mixture of cyclohexane and methylcyclohexane in any ratio.

  Particularly advantageous organic solvents include methylcyclohexane, cyclohexane, methylcyclopentane and cyclopentane and mixtures thereof. Very particular preference is given to mixtures from methylcyclopentane and cyclopentane or from methylcyclohexane and cyclohexane.

  Very particular preference is given to extractants comprising or consisting of water and the particularly preferred organic solvents mentioned above.

  In a special embodiment, an extractant containing or consisting of methylcyclohexane and water is used as an extractant for crude N-vinylpyrrolidone.

  A mixture of crude N-vinyl pyrrolidone and water has a solubility gap under suitable extraction conditions with methylcyclohexane. Solubility gaps in ternary systems are generally identified by changes in concentration and can be represented in a triangular diagram.

About the performance of the extraction In general, a temperature range of 20-100 ° C. under standard pressure (1 bar) is also suitable for the extraction of crude N-vinylamide. Extraction can also be performed at elevated pressure or reduced pressure. The extractant can be used, for example, in an amount of 20 to 0.5 parts by weight, in particular 10 to 1 parts by weight, per 1 part by weight of crude N-vinylpyrrolidone.

  When suitable extraction conditions are crude N-vinylpyrrolidone, ternary system from water and methylcyclohexane, 1 bar and 10-50% by weight of crude N-vinylpyrrolidone, particularly preferably 20-40% by weight, methylcyclohexane 20 20 to 100 ° C., particularly preferably 30 to 80 ° C., in a mass proportion of ˜80% by weight, particularly preferably 30 to 70% by weight and water 2 to 50% by weight, particularly preferably 10 to 30% by weight. Born within the temperature range of.

  Correspondingly, the extraction is carried out with a ternary system from crude N-vinylpyrrolidone, water and methylcyclohexane, preferably in compliance with the preceding extraction conditions.

  The extraction can be carried out batchwise or continuously.

  In the case of batch extraction, in a simple case, a stirred vessel for mixing two phases (extractant and the phase to be extracted) and the two phases are divided into an upper layer and a lower layer according to their density A (mixer-settler) separator is used. The solvent can then be purified, for example by distillation, and returned to the mixer again.

  The extraction is preferably carried out continuously. In particular, the entire production process is carried out continuously, including conversion of the starting materials in the reactor and subsequent workup.

  For continuous implementation of the extraction, a mixer setra or a cascade of mixer-settlers as described above is likewise suitable; in an advantageous embodiment, if it is carried out continuously, a column, for example a conventional extraction column For example, spray tray towers, sieve tray towers, extraction towers with irregular packing, pulse towers or rotating towers are used. The starting components are supplied via a so-called distributor. The distributor is an internal structure in the tower, which causes the best possible distribution of components across the tower cross section. Preferably, a suitable distributor is mounted horizontally on the column.

  Continuous extraction can be carried out in one or more columns. For the ternary crude N-vinylpyrrolidone / water / methylcyclohexane, for example, the practice of extraction in an extraction column and a wash column connected to it is taken into account. In the extraction column, undesired by-products are separated from the water / crude N-vinylpyrrolidone mixture by methylcyclohexane; in the wash column, N (which is undesirably) is also transferred to the methylcyclohexane phase. -Vinylpyrrolidone is again recovered with water. The water / N-vinyl pyrrolidone mixture separated in the washing tower can be returned to the extraction tower.

  In a preferred embodiment, continuous extraction is carried out in the column.

  The supply of crude NVP, extractant and optionally water may take place at any point in the tower. Crude NVP, extractant and optionally water may be fed separately or together and all three components or two of the three components can be fed at any point in the column at the same time.

  Preferably, the extractant (methylcyclohexane) is fed via the distributor at the bottom of the column and water is fed via the distributor at the top of the column, while the crude N-vinylpyrrolidone to be extracted. Is supplied in the middle part. Depending on the density of the components, the extractant methylcyclohexane rises to the top of the column and the extractant is enriched with by-products to be extracted from the crude N-vinylpyrrolidone and to it with N-vinylpyrrolidone. At the top of the column, N-vinylpyrrolidone is washed from methylcyclohexane with water, so that at the top, a mixture of methylcyclohexane and extracted by-products, substantially free of N-vinylpyrrolidone, is removed. be able to. At the bottom of the column, a mixture of purified crude N-vinylpyrrolidone and water is removed.

  The temperature profile generated in the column in this case depends on the mixing enthalpy of the components and the distribution of the components in the column. In the case of ternary crude N-vinylpyrrolidone / water / methylcyclohexane, the temperature in the column is preferably 10 to 90 ° C., in particular 20 to 60 ° C. and particularly preferably 30 to 50 ° C.

  Methylcyclohexane can subsequently be purified by distillation and used again.

  The water / crude N-vinylpyrrolidone mixture can also be further worked up.

  Crude N-vinyl amide purified by extraction, in particular crude N-vinyl pyrrolidone, no longer contains any fluorescent by-products. After separation of water, the content is less than 0.5 parts by weight, in particular less than 0.1 parts by weight and particularly preferably less than 0.05 parts by weight, based on 100 parts by weight of N-vinylpyrrolidone. Or less than 0.01 parts by mass.

Examples N-vinyl pyrrolidone was prepared by reaction of acetylene and 2-pyrrolidone. High boilers were separated from the resulting mixture by distillation. N-vinylpyrrolidone still containing fluorescent impurities was obtained as the top product, which was used as crude N-vinylpyrrolidone in subsequent extraction tests.

  200 ml of crude N-vinylpyrrolidone (crude NVP), 200 ml of water and 200 ml of the solvent listed in Table 1 as the extractant were mixed vigorously and shaken. An aqueous phase and an organic phase were obtained. The phases were separated and the fluorescence of the aqueous phase containing N-vinylpyrrolidone (extracted NVP) was measured.

The measured fluorescence (F) of crude N-vinylpyrrolidone was expressed as the ratio of the resulting aqueous phase to the fluorescence:
F = F Crude NVP / F Extracted NVP.

  The higher the value of F, the better the achieved separation of the fluorescent impurities. The value of F is listed in Table 1.

  Measurements were performed using a Perkin Elmer luminescence spectrophotometer LS50-B. The substance to be tested was packed in a UV cell (d = 1.0 cm) and the wavelength at which maximum fluorescence emission occurred at three different excitation wavelengths was measured. The intensity of the maximum fluorescence was expressed as a ratio of the crude NVP to the intensity of the maximum fluorescence.

Temperature: 20 ° C
Excitation wavelength λex = 320 nm, 340 nm and 360 nm
Excitation wavelength / emission wavelength gap width: 5 nm / 5 nm

Claims (17)

  In the method for separating a by-product from a product mixture rich in N-vinylamide (crude N-vinylamide), the extraction of the crude N-vinylamide is carried out using an organic solvent as an extractant. Method. The N-vinylamide is a cyclic N-vinylamide (vinyl lactam) or a formula

The process according to claim 1, characterized in that it is an acyclic N-vinylamide, wherein R1 and R2 are independently of each other an H atom or a C1-C10 alkyl group.   The acyclic N-vinylamide of formula I is N-vinylformamide (R1 and R2 = H) or N-vinyl-N-methylacetamide (VIMA, R1 and R2 = methyl). The method according to 1 or 2.   The cyclic N-vinylamide is N-vinylpiperidone, N-vinylcaprolactam or N-vinylpyrrolidone or a derivative thereof such as N-vinylmethylpyrrolidone, N-vinyldimethylpyrrolidone or N-vinylethylpyrrolidone. The method according to claim 1 or 2.   The method according to any one of claims 1 to 4, wherein the N-vinylamide is N-vinylpyrrolidone.   6. The process according to claim 1, wherein the crude N-vinylamide comprises at least 50% by weight of N-vinylamide.   7. Process according to any one of claims 1 to 6, characterized in that the crude N-vinylamide was obtained by reaction of starting material with acetylene and optionally subsequent workup.   8. The process according to claim 1, wherein the crude N-vinylamide is crude N-vinylpyrrolidone obtained by reaction of 2-pyrrolidone (γ-butyrolactam) with acetylene and optionally subsequent workup. The method of any one of Claims.   The method according to any one of claims 1 to 8, wherein distillation (crude distillation) is carried out to separate high boilers from the crude N-vinylamide before the extraction.   10. The process according to claim 1, wherein an aliphatic solvent or an alicyclic solvent is used.   The process according to claim 1, wherein the extraction is carried out with the addition of water.   12. The process as claimed in claim 1, wherein the crude N-vinylpyrrolidone is extracted with methylcyclohexane with addition of water.   The process according to any one of claims 1 to 12, characterized in that the extraction is carried out in a temperature range of 20 to 100 ° C.   14. A process according to any one of the preceding claims, characterized in that the extraction is carried out continuously in one or more columns.   Crude N-vinylpyrrolidone is extracted in the column continuously with methylcyclohexane with addition of water, with water being passed through the distributor to the top of the column and methylcyclohexane via the distributor. The method according to claim 1, wherein the crude N-vinylpyrrolidone is fed into the lower part of the column and into the middle part of the column.   At the top of the column, withdrawing a mixture from methylcyclohexane and separated by-products, and at the bottom of the column, taking out a mixture from purified crude N-vinylpyrrolidone and water. The method according to claim 15.   The fluorescent by-product is removed from the crude N-vinylamide by the extraction to a content of less than 0.05 parts by mass with respect to 100 parts by mass of N-vinylpyrrolidone. The method according to any one of up to 16.